Mechanical and chemical-mechanical planarization processes (collectively, “CMP”) remove material from the surfaces of micro-device workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a carrier head 30, and a polishing pad 40. The CMP machine 10 may also have an under-pad 25 between an upper surface 22 of the platen 20 and a lower surface of the polishing pad 40. A drive assembly 26 rotates the platen 20 (as indicated by arrow F) and/or reciprocates the platen 20 back and forth (as indicated by arrow G). Because the polishing pad 40 is attached to the under-pad 25, the polishing pad 40 moves with the platen 20 during planarization.
The carrier head 30 has a lower surface 32 to which a microfeature workpiece 50 may be attached, or the workpiece 50 may be attached to a resilient pad 34 under the lower surface 32. The carrier head 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 36 may be attached to the carrier head 30 to impart rotational motion (as indicated by arrow J) and/or reciprocal motion (as indicated by arrow 1) to the microfeature workpiece 50.
The polishing pad 40 and a polishing solution 60 define a polishing or planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the microfeature workpiece 50. The polishing solution 60 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the microfeature workpiece 50, or the polishing solution 60 may be a “clean” nonabrasive solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on non-abrasive polishing pads, and clean non-abrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the microfeature workpiece 50 with the CMP machine 10, the carrier head 30 presses the workpiece 50 facedown against the polishing pad 40. More specifically, the carrier head 30 generally presses the microfeature workpiece 50 against the polishing solution 60 on a polishing surface 42 of the polishing pad 40, and the platen 20 and/or the carrier head 30 moves to rub the workpiece 50 against the polishing surface 42. As the microfeature workpiece 50 rubs against the polishing surface 42, the polishing medium removes material from the face of the workpiece 50.
During many of the CMP processes conducted to form a typical microfeature workpiece, it is necessary to stop the material removal process at a selected plane of the microfeature workpiece 50. Accordingly, existing processes include disposing a stop layer at the selected plane in the microfeature workpiece 50. The chemical makeup of the polishing solution 60 is then chosen to (a) preferentially remove material overlaying the stop layer, and (b) stop removing material from the workpiece 50 when the stop layer is exposed. For example, polysilicon has been proposed as a stop layer material when positioned adjacent to an oxide layer, and one proposed polishing solution 60 includes a non-ionic surfactant that selectively removes the oxide and then stops the material removal upon exposing the underlying polysilicon stop layer. Further details of methods and solutions for carrying out such a process are disclosed in an article titled “Effects Of Non-Ionic Surfactants On Oxide-To-Polysilicon Selectively During Chemical Mechanical Polishing,” (Lee et al., J. of the Electrochemical Society, Jun. 17, 2002) incorporated herein in its entirety by reference.
Polysilicon has other functions in a typical microfeature workpiece 50. For example, many conventional microfeature workpieces 50 include doped polysilicon as a component for forming conductive and/or semiconductive microelectronic structures. One problem associated with conventional methods for planarizing doped polysilicon is that such methods tend to leave defects in the planarized polysilicon surface. These defects can include holes, pits, divots, or other non-uniformities that adversely affect the performance of the conductive via or other structure formed from the polysilicon. One approach to addressing this problem is to reduce the level of doping in the polysilicon. A drawback with this approach is that it can adversely affect the conductivity of the polysilicon, and therefore the performance of devices formed from the polysilicon. Another approach to addressing this drawback is to adjust some process conditions at which the polysilicon is deposited on the microfeature workpiece 50. A drawback with this approach is that it can increase the time required to complete the deposition process and can accordingly increase the cost of producing devices from the microfeature workpiece 50.